Estimation of Diffractive Surface Profile using Phase Retrieval Techniques

Abstract

An intraocular lens (IOL) is an artificial lens that is inserted into the eye as part of a treatment for cataract or myopia. Among the many types of IOLs, multifocal IOLs with diffractive optics design have been demonstrated to provide superior vision for both distance and near vision after surgery. In this dissertation, methods for estimating the diffractive surface profile of a multifocal diffractive IOL are investigated. Traditionally, several types of instruments have been proposed to determine the phase profile, such as conventional interferometers and Shack-Hartmann sensor. Holography-based setups have also been widely used for surface profile measurement. However, the proposed conventional methods require additional optical components or a reference beam, increasing system complexity and cost of the system. To avoid the limitations of the conventional system stated above, phase retrieval technique is implemented to estimate the diffractive surface profile of an IOL. The phase retrieval technique is the process of recovering the complex-valued function given the magnitude of its Fourier transform. It is natural to investigate the phase of an object, as optical imaging devices only measure the intensity of light and cannot measure the associated phase directly. This dissertation examines several phase retrieval algorithms. The multiplane phase retrieval algorithm described by Gerchberg is implemented for embodiment of the methods. To acquire multiple diffraction patterns, some techniques were used, such as displacing the imaging sensor to record intensities at different planes, modulating phase in Fourier domain using spatial light modulator (SLM) to record a sequence of intensities with different image planes, and modulating phase in pupil plane using SLM to record diffraction patterns at an image plane with phase diversity. Employing the considered phase retrieval schemes, the phase profile of diffractive multifocal intraocular lens was estimated. This dissertation begins with background section, which describes the human eye and basic principles of multifocal intraocular lenses. Chapter 1 covers basic optical structure of the human eye, age-related eye conditions, and fundamentals of intraocular lenses. Chapter 2 motives and describes several basic phase retrieval algorithms and limitations in finding the phase profile of the diffractive surface of an intraocular lens, followed by computational simulations. Chapter 3 deals with phase retrieval technique employed in combination with the multi-plane phase retrieval method, as well as the selected SLM-based phase retrieval technique suitable for finding phase profile of the diffractive intraocular lens. Chapter 4 describes the experimental setup employed for validating the phase retrieval technique to measure the wavefront profile of the intraocular lenses. The calibration procedure implemented in the experiment is discussed. Chapter 5 concludes the dissertation.